Monolithic, linear glass polarizer and attenuator

ABSTRACT

The disclosure is directed to an element that is capable of acting as both an optical polarizer and an optical attenuator, thus integrating both functions into a single element. The element comprises a monolithic or one piece glass polarizer (herein also call the “substrate”), a multilayer “light attenuation or light attenuating” (“LA”) coating that has been optimized for use at selected wavelengths and attenuations deposited on at least one polarizer facial surface, and a multilayer anti-reflective (AR) coating on top of the LA coating. The disclosure is further directed to an integrated optical isolator/attenuator comprising a first and a second polarizing elements and a Faraday rotator for rotating light positioned after the first polarizing element and before the second polarizing element, the integrated optical isolator/attenuator both polarizing and attenuation a light beam from a light source.

PRIORITY

This application is a divisional of and claims the benefit of priorityunder 35 U.S.C. §120 of U.S. application Ser. No. 14/069,789 filed onNov. 1, 2013, which claims the benefit of priority under 35 U.S.C. §119of U.S. Provisional Application Ser. No. 61/728,482 filed on Nov. 20,2012, the content of which is relied upon and incorporated herein byreference in its entirety.

FIELD

The disclosure is directed to an integrated monolithic linear polarizerand attenuator that is made by integrating two different opticalelements, a polarizer and attenuation filter, into a single element thatis both polarizing and attenuating. The element is operative in nearinfrared (NIR) at wavelengths in the range of 1275 nm to 1635 nm.

BACKGROUND

Telecommunications equipment uses both attenuators and opticalisolators. The attenuators can be used either temporarily to test powerlevels by adding a calibrated amount of signal loss or they can beinstalled permanently to properly match transmitter and receiver powerlevels. Fiber-optic telecommunication systems need a certain amount ofoptical power to work properly, but too much power can cause problems.There are cases where power may need to be restricted, for example, whencouplers do not distribute signals evenly or to protect sensitiveinstruments. Attenuators discard surplus optical power and they canreduce signal levels in communication systems to those that thereceivers can handle best. This makes it possible for all terminals in anetwork to use the same transmitters and receivers, even though lighttraveling between them suffers different losses. Adding attenuators alsomakes it possible to use the same terminal equipment in all parts of alocal network. The terminal next to the distribution node might receivea signal 20 dB higher than one on the opposite corner of the building,but an attenuator can balance the power levels. The most common andleast costly attenuators are filters that block a fixed portion of thein-coming light. These attenuators are installed in communicationsystems to balance power levels, and normally these attenuators will notneed to be changed again.

Optical isolators are used to prevent back-reflections and other noisefrom reaching sensitive optical components in telecommunicationssystems. They act as one-way paths through which the telecommunication'sfrequency light passes. Optical isolators consist of, in sequence, afirst or input polarizer, typically one with a vertical polarizationaxis to enhance the contrast ration and clean the vertically polarizedincoming light, a Faraday rotor for receiving the vertically polarizedlight and rotating it by 45°, and a second or output polarizer whosepolarization axis is at 45° to the polarization axis of the firstpolarizer. The 45° rotated light from the Faraday rotator completelypasses through the second polarizer to a receiver with virtually nolosses, for example, an optical fiber or an analyzer. If any light isreflected backwards by receiver, the second polarizer will polarizer theback-reflected light by 45° and Faraday rotator will rotate the lightfrom the second polarizer by an additional 45°. The back-reflected lightemerging from the rotator has become horizontally polarized and will beblocked by the first polarizer that permits the passage of onlyvertically polarized light. Thus, any reflected light that travels inthe direction opposite that of the incoming light will be extinguished.Optical isolators are important components in high-performance systemsbecause of the way they can block noise traveling in the wrong directionthrough the fiber.

At the present time there is no single, integrated element, that canaccomplish both these tasks; that is, act as an optical attenuator andas an optical isolator. The present disclosure provides such an elementand a device that uses the element.

SUMMARY

The disclosure is directed to an element that is capable of acting asboth an optical polarizer and an optical attenuator, thus integratingboth functions into a single element. The element comprises a monolithicor one piece glass polarizer (herein also call the “substrate”), amultilayer “light attenuation or light attenuating” coating LA that hasbeen optimized for use at selected wavelengths and attenuationsdeposited on at least one polarizer facial surface, and a multilayeranti-reflective, AR, coating on top of the LA coating, resulting in thesequence “substrate/LA/AR”. The LA coating is designed to reduce orremove excess energy in an optical system by decreasing the transmissionlevels of the incident light energy. The AR coating reduce surfacereflection losses, improves contrast and boosts transmission through theoptical surface. The combination of LA and AR coatings on the surface ofa polarizing optical substrate results in an integrated opticalpolarizer/attenuator that also prevents backscatter of light in opticaltransmission systems.

While in one embodiment the LA and AR coating are deposited on onesurface of the polarizer, in another embodiment the LA and AR coatingsare deposited on both polarizer surfaces. In a further embodiment theelement comprises a glass polarizer having a SiO₂ coating deposited onat least one polarizer surface, an LA coating that has been optimizedfor use at selected wavelengths and attenuations deposited on top of theSiO₂ coating, and an anti-reflective (AR) coating on the surface of theLA coating, resulting in the overall sequence of substrate/SiO₂/LA/AR.In an additional embodiment the LA and AR coatings are applied to onesurface of the polarizer and an AR coating only is applied to the second

The anti-reflective, AR, coating is a multilayer coating comprisingalternating layers of a high refractive index material, H′, having arefractive index greater than 1.7 and a layer of a low refractive indexmaterial, L′, having a refractive index of less than or equal to 1.7. Ina further embodiment a sealing or capping layer of SiO₂ can be placed ontop of the last deposited layer of the anti-reflective coating when thelast deposited layer of the anti-reflective coating is not SiO₂. Thelight attenuating coating LA is a multilayer coating consisting aplurality of layers HL of selected attenuating materials, where H is ahigh refractive index material and L is a low refractive index material.In the Examples given herein the multilayer LA coating comprises ITO(indium tin oxide), Si and Cr₂O₃, the ITO layer being the first layerdeposited on the polarizing glass substrate, or on a SiO₂ layerdeposited on the polarizing glass substrate prior to the deposition ofthe ITO layer. The attenuation of the element can be set to any desiredattenuation level by changing the thickness and/or number of attenuatingmaterial layers. Further, the order in which the attenuation layers aredeposited can be changed from HL as exemplified herein, to LH.

In an aspect the disclosure is also directed to an opticalisolator/attenuator device for use at telecommunications frequencies,the optical isolator/attenuator comprising a Faraday rotator having afirst end and a second end, and a polarizing element at each of saidends, at least one of said polarizing elements being a monolithicpolarizing/attenuating element. In an embodiment both of the opticalisolator/attenuator device polarizing elements are a monolithicpolarizing/attenuating element.

In one embodiment the polarizer/attenuator of the disclosure, and anoptical isolator using such polarizer/attenuator element is operative inthe wavelength range of 1275 nm to 1635 nm. In another embodiment thepolarizer/attenuator of the disclosure, and an optical isolator usingsuch polarizer/attenuation is operative in the wavelength range of 600nm to 1100 nm. In a further embodiment the polarizer/attenuator of thedisclosure, and an optical isolator using such polarizer/attenuation isoperative in the wavelength range of 1700 nm to 2000 nm. In anadditional embodiment the polarizer/attenuator of the disclosure, and anoptical isolator using such polarizer/attenuation is operative in thewavelength range of 2000 nm to 2300 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of an element that is a monolithic glasspolarizer with an integrated attenuating functionality, the elementcomprising a glass polarizer 10, an inorganic light attenuating coating,or LA coating, 12, also called herein an attenuation coating or film 12,that is optimized for the desired degree (percentage) attenuation andwavelengths of the incoming light, and an anti-reflective coating orfilm 14.

FIG. 2 is graph illustrating of percentage transmission versuswavelength of the integrated linear polarizer and attenuator atattenuations of 0, 1, 1.5, 2.0, 2.5. and 3.0 dB that represented by thecurves, 20, 22, 24, 26, 28 and 30, respectively

FIG. 3 illustrates the spectral reflectance of a polarizer havingnon-attenuating, 4-layer AR coating.

FIG. 4 illustrates the spectral reflectance of polarizer having a4-layer, 15% attenuating LA coating and a 4-layer AR coating on top ofthe LA coating.

FIG. 5 illustrates the absorbance of a polarizer having a 4-layer, 15%attenuating LA coating and a 4-layer AR coating on top of the LAcoating.

FIG. 6 is illustrates the spectral reflectance of a polarizer having a4-layer LA, 24% attenuating coating and a 4-layer AR coating on top ofthe LA coating.

FIG. 7 is illustrates the absorbance of a polarizer having a 4-layer,15% attenuating LA coating and a 4-layer AR coating on top of the LAcoating.

FIG. 8 illustrates the spectral reflectance (Rx) and the transmittance(Tx) of 5-layer 15% absorbing AR coating on a Polarlor substrate, alsocalled “Polarcor sub”, with backside effect ignored and wavelengthsranging from 620 nm to 650 nm. The 15%-absorbing LA/AR coating design isPolarcor sub_225 nm ITO_135 nm Cr₂O₃ _(_)232 nm SiO₂ _(_)93 nm Nb₂O₅_(_)333 nm SiO₂ _(_)air.

FIG. 9 illustrates the reflectance (Rx) and the transmittance (Tx)of5-layer 24% absorbing AR coating on A Polarlor substrate with backsideeffect ignored and wavelengths ranging from 620 nm to 650 nm. The24%-absorbing LA/AR coating design is Polarcor sub_229 nm ITO_79 nmCr₂O₃ _(_)213 nm SiO₂ _(_)101 nm Nb₂O₅ _(_)326 nm SiO₂ _(_)air.

FIG. 10 illustrates the spectral reflectance (Rx) and the transmittance(Tx) of 5-layer 15% absorbing AR coating on a Polarlor substrate withbackside effect ignored and wavelengths ranging from 780 nm to 820 nm.The 15%-absorbing LA/AR coating design is Polarcor sub_309 nm ITO_280 nmCr₂O₃ _(_)287 nm SiO₂ _(_)167 nm Nb₂O₅ _(_)390 nm SiO₂ _(_)air.

FIG. 11 illustrates the spectral reflectance (Rx) and the transmittance(Tx) of 5-layer 24% absorbing AR coating on Polarlor substrate withbackside effect ignored and wavelengths ranging from 780 nm to 820 nm.The 24%-absorbing LA/AR coating design is Polarcor sub_347 nm ITO_551 nmCr₂O₃ _(_)239 nm SiO₂ _(_)129 nm Nb₂O₅ _(_)392 nm SiO₂ _(_)air.

FIG. 12 illustrates the spectralreflectance (Rx) and the transmittance(Tx) of 5-layer 15% absorbing AR coating on Polarlor substrate withbackside effect ignored and wavelengths ranging from 1010 nm to 1110 nm.The 15%-absorbing LA/AR coating design is Polarcor sub_455 nm ITO_477 nmCr₂O₃ _(_)319 nm SiO₂ _(_)162 nm Nb₂O₅ _(_)526 nm SiO₂ _(_)air.

FIG. 13 illustrates the reflectance (Rx) and the transmittance (Tx) of5-layer 24% absorbing AR coating on Polarlor substrate with backsideeffect ignored and wavelengths ranging from 1010 nm to 1110 nm. The24%-absorbing LA/AR coating design is Polarcor sub_666 nm ITO_1010 nmCr₂O₃ _(_)36 nm SiO₂ _(_)546 nm Nb₂O₅ _(_)574 nm SiO₂ _(_)air.

FIG. 14 illustrates a polarizer/attenuator element comprising apolarizer 80 having an absorbing LA/AR coating 82 as disclosed hereinapplied to frontside surface F of polarizer substrate 80 and an AR(only) coating 84 applied to the backside surface B of polarizer 80.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details may beset forth in order to provide a thorough understanding of embodiments ofthe invention. However, it will be clear to one skilled in the art whenembodiments of the invention may be practiced without some or all ofthese specific details. In other instances, well-known features orprocesses may not be described in detail so as not to unnecessarilyobscure the invention. In addition, like or identical reference numeralsmay be used to identify common or similar elements.

Herein the terms “substrate”, “polarizing substrate” and “Polarcor sub”are used to define any glass or glass element that is of itself anoptical polarizer. Such glass polarizers are commercially available froma number of sources. Herein commercially available Polarcor® opticalpolarizers (Corning Incorporated, Corning, N.Y.) are used as exemplarysubstrates to make the integrated polarizing and attenuating opticalelements of this disclosure. Also herein, with reference to thecoating(s) applied to the monolithic linear glass polarizer, thecoatings and individual layers of a multilayer coating are adherent tothe polarizer glass, a previously applied coating, or a previouslyapplied layer of a multilayer coating without the use of any adhesivematerial or interlayer material between the polarizer and a coating, orthe layers of a coating, or adjacent coatings. An adhesive material istypically a liquid or a semi-liquid that bonds items together andrequire curing (hardening) by either evaporating a solvent or bychemical reactions that occur between two or more constituents of theadhesive—glues and epoxy resins being examples. Interlayer materials aretypically polymeric materials that can hold or bond together twodifferent items without curing—double stick tape being an example.Further, herein the term “metal oxide” means an oxide consisting of onemetal and oxygen, for example Cr₂O₃, Al₂O₃, GeO₂, et cetera, andmixed-metal oxide mean an oxide consisting of at least two metals andoxygen, for example, indium-tin-oxide and SrTiO₃.

The device of the present disclosure is directed to an element that hasintegrated polarizing and attenuating functions, and can be used to makean integrated optical isolator/attenuator when combined with a Faradayrotator. Optical isolators utilize optical polarizers in combinationwith a Faraday rotor to reduce or eliminate back-reflectance intelecommunications systems. Optical polarizers of the type used hereinare classified as monolithic and absorptive type glass polarizers whichare optimized for telecommunication related wavelengths. Opticalpolarizers are well described in the art; for example, U.S. Pat. Nos.7,648,656, 7,510,989 and 7,461,488 describe making optical polarizerscontaining various metals. Metals that can be used in the preparation ofoptical polarizers include silver, copper and copper/cadmium, andadditionally metals such as platinum, palladium, palladium, gold, andother metals. For example, Japanese Patent Application Publications2009-217176A and 2009-217177A describe making polarizers and makingoptical isolators, for example pig-tail type isolators for opticalcommunications, the isolators comprising a Faraday rotor and apolarizing element on either end of the Faraday rotor.

At the present time, in order to attenuate the optical signal emitted bytelecommunications transmission laser diodes, VOAs (variable opticalattenuators) or other optical components are used. The presentdisclosure describes an element that can act to both polarize light andattenuate light, a method of making the element, and a device thatenables achieving a desired and fixed attenuation while also acting asan optical isolator. In a polarization dependent isolator (“PDI”),optical polarizer elements are used as the input and the outputpolarizer of the isolator. In accordance with the present disclosure,the desired attenuation is achieved by placing an inorganic lightattenuating, LA, coating on top of at least one polarizer surface and ananti-reflective, AR, coating on top of the inorganic LA coating. In thepolarizing/attenuating devices described herein the polarizers can beused as the input (0 degree polarization or vertical axis) element or asthe output (45 degree polarization) element of the optical isolator. Inan embodiment the amount of attenuation is in the range of greater than0 dB to 3 dB over the wavelength range of 1275-1635 nm. In anotherembodiment the amount of attenuation can be in the range of 0.5 dB to 3dB over the wavelength range of 1275-1635 nm. The design concept ofattenuation and antireflection described herein can also be applied toother wavelength ranges by changing LA coating and AR coatingaccordingly using the teachings disclosed herein. For example, thedesign can be use at wavelength in the range of 600-1100 nm, 1700-2000nm and 2000-2300 nm. The polarizer/attenuator elements in these rangescan also be used in optical isolators.

FIG. 1 illustrates the structure of the optical element having anintegrated functionality to polarize/analyze incident polarized lightand attenuate it with a desired attenuation. The inorganic film can bedeposited on the polarizer by any of the conventional depositionmethods. The article in FIG. 1 comprises an polarizer 10, an AR coating14, and an LA film 12 that is in between the polarizer 10 and AR coating14. The LA coating film 12 is optimized for the desired degree ofattenuation and wavelengths.

In order to achieve the desired and attenuation for the operatingwavelength range of the laser diode, the LA coating can be designed andoptimized for either deposition on one side of the polarizer, ordesigned and optimized for deposition on both sides. With the use ofsuch element, a polarization dependent isolator can have an integratedfunctionally, that is, be an “isolator plus attenuator.” FIG. 2, showstypical and simulated percent transmission versus wavelength spectra forintegrated linear polarizers with attenuation of 0, 1, 1.5, 2, 2.5 and3.0 dB, respectively. which are individually represented by numerals 20,22, 24, 26, 28, and 30, respectively, located on the right. Thedifferent attenuations are dependent on the thickness of the attenuatingcoating that is applied on the polarizer and the composition of theattenuating coating.

FIG. 3 illustrates the spectral reflectance of a polarizer having only anon-attenuating, 4-layer AR coating on a Polarcor® substrate and noattenuation coating. This AR-coated polarizer serves as the baselineexample for a polarizer with an AR coating, but no attenuating coating.The designed AR coating, beginning with the substrate and ending withair, is: (1) substrate, and (2) AR coating: 51 nm Nb₂O₃, 56 nm SiO₂, 248nm Nb₂O₅, 236 nm SiO₂, air. Polarizers with an LA/ARattenuation/anti-refection will be compared to this example. No cappinglayer is applied because the last layer of the AR coating is SiO₂.

FIG. 4 illustrates the spectral reflectance of a polarizer/attenuatorelement having an 8-layer 15% attenuating coating comprising a 4-layerLA coating and a 4-layer (AR coating on top of the LA coating. Theoverall coating design of the 15% absorbing polarizer/attenuatorelement, beginning with the substrate, is: (1) substrate, (2) multilayerLA coating: 317 nm ITO, 22 nm Si, 67 nm Cr₂O₃, 177 nm Si, and (3)multilayer AR coating: 545 nm Nb₂O₅, 100 nm SiO₂, 111 nm Nb₂O₅, 310 nmSiO₂, air; where ITO is indium-tin-oxide. No capping layer is appliedbecause the last layer of the AR coating is SiO₂.

FIG. 5 illustrates the spectral absorbance of a polarizer/attenuatorelement having an 8-layer 15% attenuating coating comprising a 4-layerLA coating and a 4-layer AR coating on top of the LA coating. Theoverall coating design of the 15% polarizer/attenuator element is thesame as that of FIG. 4, and beginning with the substrate, it is: (1)substrate, (2) multilayer LA coating: 317 nm ITO, 22 nm Si, 67 nm Cr₂O₃,177 nm Si, and (3) multilayer AR coating: 545 nm Nb₂O₅, 100 nm SiO₂, 111nm Nb₂O₅, 310 nm SiO, air; where ITO is indium-tin-oxide. No cappinglayer is applied because the last layer of the AR coating is SiO₂.

FIG. 6 is illustrates the spectral reflectance of a polarizer/attenuatorelement having an 8-layer 24% attenuating coating comprising a 4-layerLA coating and a 4-layer AR coating. The overall coating design of the24% polarizer/attenuator element, beginning with the substrate, is: (1)substrate, (2) multilayer LA coating: 535 nm ITO, 21 nm Si, 120 nmCr₂O₃, 244 nm Si, and (3) AR coating: 539 nm Nb₂O₅, 188 nm SiO₂, 62 nmNb₂O₅, 369 nm SiO₂, air; where ITO is indium-tin-oxide. No capping layeris applied because the last layer of the AR coating is SiO₂.

FIG. 7 is illustrates the spectral absorbance of a polarizer/attenuatorelement having an 8-layer, 24% absorbing coating comprising a 4-layer LAcoating and a 4-layer AR coating on top of the LA coating. The overallcoating design of the 24% absorbing coating is the same as that of FIG.6, and beginning with the substrate it is: (1) substrate, (2) multilayerLA coating: 535 nm ITO, 21 nm Si, 120 nm Cr₂O₃, 244 nm Si, and (3)multilayer AR coating 539 nm Nb₂O₅, 188 nm SiO₂, 62 nm Nb₂O₅, 369 nmSiO₂, air; where ITO is indium-tin-oxide. No capping layer is appliedbecause the last layer of the AR coating is SiO₂.

FIGS. 8-13 illustrate the spectral reflectance and the transmittance ofadditional polarizer/attenuator elements with the backside effectignored. The “backside effect” refers to reflectance that occurs at thesurface furthest from where the light first enters thepolarizer/attenuator element. The reason for excluding the backsideeffect from FIGS. 8-13 is to determine and show the real effect of theenginnered absorbing LA/AR coating applied to the frontside surfacewhere the light enters polarizer/attenuator element. The backsidereflection can be eliminated by applying an AR coating on the backsideof the polarizer or by application of the absorbing LA/AR coatingdescribed earlier herein. The element in FIG. 14 illustrates apolarizer/attenuator element comprising a polarizer 80 having anabsorbing LA/AR coating 82 as disclosed herein applied to frontsidesurface F of polarizer substrate 80 and an AR (only) coating 84 appliedto the backside surface B of polarizer 80. Light hv impinges on thefrontside surface of absorbing LA/AR coating 82 where it is attenuatedby coating 82. The light then passes through the polarizer 80 where itis polarized, and the polarized light then passes through the backsidesurface B of polarizer 80 which can have an AR coating 84 coatingapplied In FIG. 14 numeral 86 represents any light that may be reflectedfrom the frontside surface F and numeral 88 indicates any light that isreflected from the backside surface B. Thus, using the teachings of thisdisclosure, one can prepare a polarizer/attenuator have a LA/AR coatingon one or both of the polarizer substrate 80's surfaces, or an LA/ARcoating on polarizer 80's frontside surface and an Ar coating only onthe polarizer 80's backside surface.

FIG. 8 illustrates the spectral reflectance and transmittance of 5-layer15% absorbing AR coating on a Polarlor substrate, also called “Polarcorsub”, with backside effect ignored and wavelengths ranging from 620 nmto 650 nm. The 15%-absorbing LA/AR coating design is Polarcor sub_225 nmITO_135 nm Cr₂O₃ _(_)232 nm SiO₂ _(_)93 nm Nb₂O₅ _(_)333 nm SiO₂_(_)air.

FIG. 9 illustrates the spectral reflectance and transmittance of 5-layer24% absorbing AR coating on A Polarlor substrate with backside effectignored and wavelengths ranging from 620 nm to 650 nm. The 24%-absorbingLA/AR coating design is Polarcor sub_229 nm ITO_79 nm Cr₂O₃ _(_)213 nmSiO₂ _(_)101 nm Nb₂O₅ _(_)326 nm SiO₂ _(_)air.

FIG. 10 illustrates the spectral reflectance and transmittance of5-layer 15% absorbing AR coating on a Polarlor substrate with backsideeffect ignored and wavelengths ranging from 780 nm to 820 nm. The15%-absorbing LA/AR coating design is Polarcor sub_309 nm ITO_280 nmCr₂O₃ _(_)287 nm SiO₂ _(_)167 nm Nb₂O₅ _(_)390 nm SiO₂ _(_)air.

FIG. 11 illustrates the spectral reflectance and transmittance of5-layer 24% absorbing AR coating on Polarlor substrate with backsideeffect ignored and wavelengths ranging from 780 nm to 820 nm. The24%-absorbing LA/AR coating design is Polarcor sub_347 nm ITO_551 nmCr₂O₃ _(_)239 nm SiO₂ _(_)129 nm Nb₂O₅ _(_)392 nm SiO₂ _(_)air.

FIG. 12 illustrates the spectral reflectance and transmittance of5-layer 15% absorbing AR coating on Polarlor substrate with backsideeffect ignored and wavelengths ranging from 1010 nm to 1110 nm. The15%-absorbing LA/AR coating design is Polarcor sub_455 nm ITO_477 nmCr₂O₃ _(_)319 nm SiO₂ _(_)162 nm Nb₂O₅ _(_)526 nm SiO₂ _(_)air.

FIG. 13 illustrates the spectral reflectance and transmittance of5-layer 24% absorbing AR coating on Polarlor substrate with backsideeffect ignored and wavelengths ranging from 1010 nm to 1110 nm. The24%-absorbing LA/AR coating design is Polarcor sub_666 nm ITO_1010 nmCr₂O₃ _(_)36 nm SiO₂ _(_)546 nm Nb₂O₅ _(_)574 nm SiO₂ _(_)air.

While there are different methods that can be used to prepare theintegrated isolator/attenuator of this disclosure, one requirement thatmust be fulfilled is that during the deposition of the attenuatingcoating and the anti-reflection coating is that the temperature of thesubstrate must be kept below the temperature at which the metallicparticles in the polarizing glass substrate will respheroidize. Themetallic particles in the polarizer are elongated and if they are heatedto too high a temperature the particles can contract and/or becomespherical particles (respheroidize) instead of remaining as elongatedparticles. If this occurs the polarizing properties of the glass willdecrease, or they can be completely lost. The temperature at which thisoccurs will differ depending on what specific metallic particles, ormixture of metallic particles are present in the glass and are impartingthe polarization properties to the glass. For example, if the polarizingmetal is silver, copper or copper/cadmium the substrate temperatureduring the deposition of the coating material(s) is less than 400° C. Inanother embodiment the coating deposition temperature is less than 350°C. In a further embodiment the coating deposition temperature is lessthan 300° C. The polarizing metal is selected from the group consistingof silver, copper or copper/cadmium. In an embodiment the polarizer, inaddition to containing a polarizing metal selected from the silver,copper or copper/cadmium further contains a noble metal selected fromthe group consisting of platinum, palladium, osmium, iridium, rhodium orruthenium as is mentioned in U.S. Pat. Nos. 7,468,148 and 7,5110,989,the noble metal being present in an amount in the range of 0.0001 wt. %to 0.5 wt. % measured as zero valent metal. The temperature at which thepolarizing metal particles in the glass will contract or respheroidizecan be experimentally determined before the coating process by heatingthe glass polarizer and observing the temperature at which contractionand/or respheroidization occurs. This process is to an extent dependenton both time and temperature. For example, contraction/respheroidizationcan occur in minutes when the polarizer is heated to 500° C. At atemperature of 400° C. the time is approximately one hour, or more.

The attenuation and anti-reflection coatings can both be applied byphysical and chemical vapor deposition methods known in the art. Asingle method can be used to apply both coatings or a different methodcan be used for different coatings if this is necessary. The depositionof the attenuating LA coating and AR coating can be done with or withoutthe use of a mask. If a mask is used it can be a regular mask, a reversemask or a partial mask which have been described in in U.S. Pat. No.7,465,681 and Patent Application No. 2009/0297812, which also describesthe use of a reverse mask and a partial mask, respectively. Someexemplary deposition methods have been described in U.S. Pat. No.7,465,681 and Patent Application No. 2009/0297812, which also describesthe use of a reverse mask and a partial mask, respectively. The methodsinclude:

(1) Conventional deposition (CD) in which the material(s) that is/are tobe deposited are heated, in vacuum, in the presence of a substrate uponwhich a coating is to be deposited, to the molten state by eitherresistance heating or electron bombardment. When molten, evaporation ofthe material(s) occurs and a coating is deposited on the substrate. Inthis method the substrate is generally heated. However, overall, thismethod is generally not well suited to making telecommunicationsdevices.

(2) Ion-Assisted Deposition (IAD) is similar to the CD method, but ithas the added feature that the coating being deposited is bombarded withenergetic ions of an inert gas, for example argon ions, during thedeposition process, plus some ionized oxygen, which in the case of oxidecoatings is generally necessary to improve the coating stoichiometry.The bombardment serves to transfer sufficient momentum to the coatingbeing deposited to overcome surface energies, provide surface mobilityand produce dense, smooth coatings. An advantage of this method is thatlittle or no substrate heating is required.

(3) Ion Beam Sputtering (MS) in which an energetic ion beam (forexample, argon ions in the range of 500 eV to 1000 ev) are directed to atarget material, typically an oxide material. The momentum transferredupon impact is sufficient to sputter-off the target material to asubstrate where it is deposited as a smooth, dense coating. However,this method also has drawbacks which limit its utility; for example, (a)deposition uniformity over the surface of the substrate can become aproblem that limits product quality; (b) as the target becomes erodedthe uniformity of the deposited coating changes; and (c) the bombardmentenergy is quite high, leading to dissociation of the deposited firm.

4) Plasma Ion Assisted Deposition (PIAD) which is similar to IAD exceptthat the momentum is transferred to the depositing coating via a lowvoltage, but high current density plasma. Typical bias voltages are inthe range of 90-160 V and current densities are in the range of mA/cm².

The deposition of the attenuating LA coating and AR coating can be donewith or without the use of a mask. In addition, the deposition of thecoating layers can be done with or without plasma ion-assistance, duringor after the deposition of the individual layers. In addition, whenoxide coatings are formed an oxygen-containing plasma can be used duringthe deposition process to insure that the deposited oxide material isnot depleted of oxygen. However, when Si(0), or simply Si, is one of thematerials used in the multilayer attenuation coating, no oxygen shouldbe present in any plasma that is used during the deposition of the Silayer. When a metal oxide is deposited on top of the Si layer oxygen canbe bled into the system during the metal oxide deposition as isexplained below in more detail.

The attenuation coating of the disclosure is a multilayer coating, thecoating materials being selected from the group consisting of metal andmixed-metal oxide materials having a refractive index “n” of greaterthan 1.7, the L layer, and silicon, Si or Si(0), with all of said metaloxides and silicon having a non-zero extinction coefficient. In anembodiment at least one layer of the metal or mixed-metal oxide materialin the attenuation coating has a refractive index greater than 2.0. Inanother embodiment the at least one layer of the metal or mixed-metaloxide material in the attenuation coating has a refractive index greaterthan 2.1. Silicon, n greater than approximately 3.4, is used in theformation of the attenuation coating. When Si is used as an attenuationcoating material it is deposited without the use of any oxygen or anyoxygen-containing plasma being used during the Si deposition step, theplasma being used to smooth and densify the film being deposited asindicated in U.S. Pat. No. 7,465,681 and Patent Application No.2009/0297812 cited above. The Si is deposited on top of an oxygencontaining material, for example, ITO as in the Examples herein. DuringSi deposition only argon or other inert gas plasma should be used. Asthe Si is laid down on top of an oxide material, the first few atomiclayers of deposited Si form a Si—O bond with oxygen atoms present at thesurface of the oxide material upon which it is being deposited, forexample, the glass polarizer substrate, a SiO₂ film deposited on thepolarizer's surface or a metal or mixed-metal oxide. Once the depositionsurface is covered with Si no further Si—O bonds can form and the Silayer is built up until it reaches the design specification. After theSi layer has been deposited an oxide material, MO, can be deposited ontop of the Si layer. As this oxide material is deposited it reacts withSi atoms at the surface of the Si layer to form Si—O-M bonds at thesurface, M being the metal in the oxide being deposited. Once a fewatomic layers of the oxide material has been deposited on top of the Silayer no further Si—O-M bonds are formed.

The attenuating coating is a multilayer coating formed using at leasttwo different materials having different refractive indices andextinction coefficients, one material being a high refractive indexmaterial H and the other being a low refractive index material L. The Hmaterial is Si and the L material is a metal or mixed metal oxide thathas a refractive index n greater than 1.7 and an extinction coefficientthan 0.001. In an further embodiment at least one of the L materials inthe multilayer attenuation coating has a refractive index greater than2.1 and an extinction coefficient greater than 0.001. The H material inthe multilayer attenuation coating is Si, refractive index greater than3.4 and an extinction greater than 0.001. Exemplary L materials that canbe used in forming the attenuation coating include indium-tin-oxide(ITO), Cr₂O₃, ZnO, Nb₂O₅ and GeO₂. The thickness of the ITO layer is inthe range of 250 nm to 600 nm. The thickness of the Si(0) layer(s) is inthe range of 20 nm to 700 nm, and the thickness of the Cr₂O₃, ZnO, Nb₂O₅and GeO₂ layer(s) is in the range of 20 nm to 200 nm. The overallthickness of the attenuation coating is in the range of 300 nm to 1500nm.

The anti-reflection coating is a multilayer oxide coating comprisingalternating layers of a high refractive index (“n”) material H′ having ngreater than 1.7 and a low refractive index material L′ having n lessthan or equal to 1.7. The high index AR coating material are selectedfrom the group consisting of ZrO₂, HfO₂, Ta₂O₅, Nb₂O₅, TiO₂, Y₂O₃,Sc₂O₃, Si₃N₄, SrTiO₃ and WO₃. The low index AR coating material isselected from the group consisting of SiO₂, fused silica, HPFS®, F-dopedSiO₂ (F-SiO₂), and Al₂O₃, and fluorides MgF₂, CaF₂, BaF₂, YbF₃, YF₃. Ifthe last deposited layer of the AR coating is not SiO₂, a sealing orcapping layer of SiO₂ can be placed on top of the last deposited layer.The thickness of the high refractive index layer(s) is in the range of50 nm to 700 nm. The thickness of the low refractive index layer(s) isin the range of 75 nm to 500 nm. The overall thickness of the AR coatingis in the range of 700 nm to 1500 nm. When a SiO₂ capping layer is usedthe thickness of the capping layer is in the range of 25 nm to 150 nm.One pair of a high refractive index layer and a low refractive indexlayer is a coating period, and the AR coating comprises at least oneperiod to a plurality of periods in the range of 2-20; thus the numberof AR coating periods is in the range of 1-20.

Thus, in one aspect this disclosure is directed to an integratedmonolithic linear polarizer/attenuator element comprising of a glasspolarizer having polarizing particles therein, a multilayer attenuationcoating deposited on at least one surface of the glass polarizer and amultilayer anti-reflection coating deposited on top of the attenuationcoating. The polarizing particles in the glass polarizer are selectedfrom the group consisting of silver, copper and copper/cadmium. In anembodiment the glass polarize further comprises a noble metal selectedfrom the group consisting of platinum, palladium, osmium, iridium,rhodium or ruthenium, said noble metal being present in an amount in therange of 0.0001 wt. % to 0.5 wt. % measured as zero valent metal. Theattenuation obtainable by the polarizer/attenuator element is in therange of greater than 0 dB to 3 dB over the wavelength range of1200-1700 nm.

The multilayer anti-reflection coating comprises a plurality of periodsH′L′, where H′ is metal oxide material having a refractive index greaterthan 1.7 and L′ is a metal oxide material having a refractive index lessthan 1.7. The high refractive index material is selected from the groupconsisting of ZrO₂, HfO₂, Ta₂O₅, Nb₂O₅, TiO₂, Y₂O₃, Sc₂O₃, Si₃N₄, SrTiO₃and WO₃. The low refractive index material is selected from the groupconsisting of SiO₂, F-doped SiO₂, and Al₃O₃, and fluorides MgF₂, CaF₂,BaF₂, YbF₃, YF₃.

In another aspect the disclosure is directed to an integrated opticalisolator/attenuator comprising:

a first and a second polarizing elements and a Faraday rotator forrotating light positioned after the first polarizing element and beforethe second polarizing element, the integrated opticalisolator/attenuator both polarizing and attenuation a light beam from alight source;

at least one of the polarizing elements is a monolithic glasspolarizer/attenuator element comprising a glass polarizer having amultilayer attenuation coating deposited on the glass polarizer and amultilayer anti-reflection coating deposited on top of the attenuationcoating;

the polarization axis of the of the second polarizing element is offsetfrom the polarization axis of the first polarizing axis element thenumber of degrees the light is rotated by the Faraday rotator; and

the optical isolator/attenuates the incoming light by an amount in therange of greater than 0 dB to 3 dB.

The integrated optical isolator/attenuator has an attenuation in therange of 0.5 dB to 3 dB and is operative in the wavelength range of1275-1635 nm. The same design concept can applied to other interestedwavelength ranges by changing LA coating and AR coating accordingly. Themultilayer attenuation coating materials are at least two materialsselected from the group consisting of metal oxides and mixed-metaloxides having an index of refraction greater than 2 and silicon, and thetotal thickness of the attenuation coating is in the range of 300 nm to1500 nm. The multilayer anti-reflection coating comprises a plurality ofperiods H′L′, where H′ is metal oxide material having a refractive indexgreater than 1.7 and L′ is a metal oxide material having a refractiveindex less than 1.7, and the total thickness of the anti-reflectioncoating is in the range of 700 nm to 1500 nm. The high refractive indexmaterial is selected from the group consisting of ZrO₂, HfO₂, Ta₂O₅,Nb₂O₅, TiO₂, Y₂O₃, Sc₂O₃, Si₃N₄, SrTiO₃ and WO₃. The low refractiveindex material is selected from the group consisting of SiO₂, F-dopedSiO₂, and Al₃O₃. and fluorides MgF2, CaF2, BaF2, YbF3 and YF3.

In an additional aspect the disclosure is directed to a method formaking an integrated monolithic linear polarizer/attenuator elementcomprising:

providing a monolithic linear glass polarizer containing elongatedmetallic polarizing particles therein;

depositing on at least one surface of the glass polarizer a multilayerattenuating coating comprising at least two different coating materialshaving a refractive index greater than 2; and

depositing a multilayer anti-reflection coating on top of theattenuation coating. the anti-reflection coating comprising at least oneperiod H″L where H′ is a high refractive index material having an indexof refraction greater than 1.7 and L′ is a low index of refractionmaterial having and index of refraction less than or equal to 1.7 tothereby form wherein during the deposition of the attenuating coatingand the anti-reflection coating, the temperature of the glass polarizeris below the temperature at which the metallic particles in thepolarizing glass substrate will contract or respheroidize.

In the method, depositing an attenuation coating means depositing amultilayer coating of attenuation coating materials selected from thegroup consisting of silicon having a refractive index n≧3.4, and metaloxides and mixed-metal oxides having an index of refraction greater than1.7; and depositing an anti-reflection coating , meaning depositing aplurality of periods H′L′, where H′ is metal oxide material having arefractive index greater than 1.7 and L′ is a metal oxide materialhaving a refractive index less than 1.7. The multilayer attenuationcoating comprises an ITO layer having a thickness in the range of 250 nmto 600 nm, a Cr₂O₃ layer having a thickness in the range of 20 nm to 200nm and at least one silicon layer having a thickness in the range of 30nm to 700 nm; and the multilayer anti-reflection coating comprises aplurality of periods H′L′, where H′ is selected from the groupconsisting of ZrO₂, HfO₂, Ta₂O₅, Nb₂O₅, TiO₂, Y₂O₃, Sc₂O₃, Si₃N₄, SrTiO₃and WO₃, and L′ is selected from the group consisting of SiO₂, F-dopedSiO₂, and Al₃O₃.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

We claim:
 1. An integrated optical isolator/attenuator comprising afirst and a second polarizing elements and a Faraday rotator forrotating light positioned after the first polarizing element and beforethe second polarizing element, the integrated opticalisolator/attenuator both polarizing and attenuation a light beam from alight source; at least one of the polarizing elements is a monolithicglass polarizer/attenuator element comprising a glass polarizer having amultilayer light attenuation, LA, coating deposited on the glasspolarizer and a multilayer anti-reflection, AR, coating deposited on topof the LA coating; the polarization axis of the second polarizingelement is offset from the polarization axis of the first polarizingaxis element by the number of degrees the light is rotated by theFaraday rotator; and the optical isolator/attenuator attenuates theincoming light by a amount in the range of greater than 0 dB to 3 dB;wherein: the multilayer IL coating materials comprise a high refractiveindex material H and at least one low refractive index material L thatare selected from the group consisting of silicon as H, and metal andmixed-metal oxides having an index of refraction greater than 1.7 as L,and the total thickness of the attenuation coating is in the range of300 nm to 1500 nm; and the multilayer AR coating comprises a pluralityof periods H′L′, where H′ is a metal oxide material having a refractiveindex greater than 1.7 and L′ is a metal oxide material having arefractive index less than or equal to 1.7, and the total thickness ofthe anti-reflection coating is in the range of 700 nm to 1500 nm.
 2. Theintegrated optical isolator/attenuator according to claim 1, wherein theattenuation is in the range of 0.5 dB to 3 dB.
 3. The integrated opticalisolator/attenuator according to claim 1, wherein theisolator/attenuator is operative in the wavelength range of 1200-1700nm.
 4. The integrated optical isolator/attenuator according to claim 1,wherein L is selected from the group consisting of ITO, Cr₂O₃, ZnO,Nb₂O₃ and GeO₂.
 5. The integrated optical isolator/attenuator accordingto claim 4, wherein at least one LA coating material L has an index ofrefraction greater than
 2. 6. The integrated monolithic linearpolarizer/attenuator element according to claim 1, wherein the AR highrefractive index material H′ is selected from the group consisting ofZrO₂, HfO₂, Ta₂O₅, Nb₂O₅, TiO₂, Y₂O₃, Si₃N₄, SrTiO₃ and WO₃.
 7. Theintegrated monolithic linear polarizer/attenuator element according toclaim 1, wherein the AR low refractive index material L′ is selectedfrom the group consisting of SiO₂, F-doped SiO₂, and Al₃O₃.